Electrometallurgy



March 18, 1924.

1,487,275 CZ. A. SCHARSCHU BLECTROHETAIQLURGY Filed Dec. 27. 1920 Fig it 6 0 if 5 Inventor:

Charles Afichars chu, y W'm His Attorney.

Patented Mar. 18, 1924.

UNITED STATES PATENT OFFICE.

CHARLES A. SCHARSCHU, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTROMETALLURGY.

Application filed December 27, 1920. Serial No. 433,147.

To all whom it may concern:

Be it known that I, CHARLES A. SCHARSGHU, a citizen of the United States, residing at Pittsfield, in the county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Electrometallurgy, of which the following is a specification.

The present invention comprises a method of and apparatus for refining stwl and other metals and particularly silicon steel; the process results in a superior product which constitutes'another aspect of my invention.

In the construction of cores for electrical apparatus, especially of the alternating current type, such as transformers and dynamoelectric machines, it is highly important to use magnetic material in which the watt losses, due to hysteresis and eddy currents, are as low as possible. Consequently efforts have been made during the development of the electrical industry to improve the mag netic properties of core material, and the substitution of silicon-iron and other alloys for ordinary steel has indeed efi'ected a considerable saving in electrical energy. Fur

' ther efforts to still more improve the magnetic properties of silicon steel have and are being made by manufacturers of this material, since it 1s realized. that a reduc tion of core loss by even a small percentage results in the savin of a large amount of energy; thus a re notion of core loss of one or two per cent is looked upon as an im ortant achievement.

ilicon steel usually contains from 3.75% to 4% silicon; it is ordinarily made in the open hearth furnace; it is cast into ingots and these are rolled into thin sheets which are used in core construction. The open hearth process results in a material in in which a considerable amount of slag is distributed throughout the mass in which the sulphur content is generally as high as from 0.03 to 0.04 per cent. I have found that the impurities carried bythe slag and especially the high sulphur content of the prodcct are detrimental characteristics of the magnetic material, since to their presonce a "large percentage of the hysteresis ac tion is due.

I have discovered that magnetic material of any kind and especially silicon steel may be made that is substantially free of slag inclusion and in which the sulphur content is leduced to and below .010 and usually as low as 0.005 per cent, and even lower where'- by the core loss is remarkably reduced, the reduction amounting on the average to about 12 per cent, and is in individual cases still greater. 7

My improved process, broadly speaking, consists in treating the material, whether 1t be scrap or when already fused by the open hearth process, in a fluid state in such manner as to exclude the admission of air; expel the occluded particles of slag from the interior of the fused mass to the surface and then pour the material from underneath the sheet of slag which, as usually, is formed on the surface. This process is preferably carried'out by the use of an induction furnace of a specific construction which constitutes a part of my invention. While the fused mass is in the induction furnace and preparatory to the practice of my invention, the material may be chemically refined. in any ordinary or improved manner.

In the accompanying drawing, Fig- 1 illustrates partly in elevation and partly in vertical section an induction furnace enrbodying structural features of my invention; Fig. 2 is a plan view of'the furnace chamber, the furnace top being removed; and Fig. 3 is a top view, the primary coil and housing being shown in part broken awa T he induction furnace shown in the drawing comprises an annular furnace crucible 1, surrounding a magnetic core 2, which has a flat primary winding 3, supplied with alternating current by conductors not shown. The primary winding may consist of annular sections, as shown; it is suitably mounted on a framework 4 above the crucible 1, in the manner set forth in Patent No. 1326120 to Un er. The furnace crucible is provided witi a refractory lining 5, which is in direct contact with the body of metal 6 to be melted, and consists preferably of particles of highly sintered' or fused magnesia molded with a binder such as magnesium sulphate to form a solid mass. This liningrests upon a wall of refractory brick 7, which in turn is supported by a suitable casing 8, made of boiler plate or the like. I have discovered that the location of the channel or crucible 1 beneath and surrounded by a shell 10 containing,

ventilating openings 11, but I wish it to he understood that these and other structural details are shown merely for the purposes of illustration.

The pouring spout 12 communicates with the furnace chamber near the bottom like the spout of a teapot, so that the fused metal may be poured from the furnace from beneath the top slag layer without causing this slag or any part of it to be mixed with the metal. The pouring spout is provided with a door 13. The charge receiving opening 14;

is similarly provided with a door (not shown). A pouring spout of this character has heretofore been suggested for use in another kind of furnace, but in the induction furnace used for the practice of my process it cooperates with the magnetic function of the apparatus to assist the removal of the occluded slag particles.

The metal to be refined may be received in a molten state from any suitable source, for example, a Bessemer converter, an open hearth furnace, or an arc furnace, and may consist of soft steel, hard steel, or any alloy steel. My invention is also applicable to the melting of cold material either as scrap or new material directly in the induction furnace. The metal is allowed to attain a. temperature of about to 150 C. in excess of its melting point and is maintained in that condition for a period of from 45 minutes to one and one-half hours in addition to the time required for chemical refinement if such is resorted to while the metal is in a fluid state in the induction furnace.

When the induction furnace is charged with scrap or raw material, the ordinary chemical refinement is practiced right there, and after the refining slag has been removed in the ordinary manner a new slag is added.

This is preferably a basic slag consisting,

for example, of lime and silica. the latter not exceeding 20%, and in some cases a small amount of fiuorspar is added to thin the slag. Any other suitable slag which is basic in character may be used. When chemically refined molten metal from any source, such as a Bessemer converter, an open hearth furnace or an arc furnace is introduced into the induction furnace, the

same procedure is observed, that is to say, a

basic slag of the general character above indicated is added.

The molten metal is subjected to the electromagnetic purifying treatment which I will now describe 1n greater detail. Owing to the location of the primary winding above the crucible element of the furnace, the alternating flux gives to the molten mass a slow but powerful movement from the inner edge of the annular channel downwardly toward the bottom and upwardly along the outer edge of the channel. In this respect the action of the flux upon the fluid metal is different from that of the magnetic flux when the primary winding is concentrio with the channel, for in the latter case the molten metal is violently agitated in an irregular manner, causing the occluded slag particles to mix continuously with the metal and effectually preventing a separation of the same. By locating the primary winding above the crucible channel, the movement of the metal becomes very much slower. There are two forces acting on the molten charge tending to expel the slag from the metal, namely, the compressive effect of the magnetic field upon the charge and the electrodynamic effect which exerts a different repellent action upon the slag and metal.

The compressive or pinch force of the magnetic field of a current-carrying conductor is a force acting radially inward u on the current-carrying elements of the con uc tor. As the slag is a poor conductor it tends to be squeezed out somewhat like water being squeezed out of a s nge. The separating action due to the e ectro-dynamic effect is somewhat comparable to the separation occurring in a centrifugal separator. The current-carrying metal is repelled with greater force than the slag particles. As the magnetic field is applied from above, the

slag particles tend to come to the surface.

Due to the combined effect of the slow and regular movement of the charge and the ex pulsive force exerted on the slag particles, they are carried with the metal to the surface and there attach themselves to the slag. In this manner the fused mass is substantially freed from slag occlusion.

My improved form of pouring spout 12 which communicates with the bottom of the crucible 1 prevents the remixing of the metal with the expelled slag when the metal is poured by tilting the furnace, so that the advantage of the preceding melting-treatment under the influence of the electromagnetic field is not lost. when the metal is poured.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The method of refining metal containing slag particles which consists in subjecting said metal in a molten state to a. period- III ically varying magnetic field adapted to cause said slag articles to rise to and remain on the sur ace and thereupon separating the metal and slag while preventing re-admix ture thereof.

2. The steps in the method of refining metal which consists in subjecting said metal in a molten state to the effect of a periodically varyin magnetic field applied from above the b0 y of metal to be pur1fied,thereby causin slag inclusions to rise to and remain at the surface, and finally separatin the purified metal from the superimpose sla layer while said layer remains undistur d. I

3. The steps in the method of refining alloys which consists in subjecting said allo s at a temperature materially in excess of t e melting point, subsequent to purification by chemically active rea ents, to a periodically varying magnetic fie d acting to separate slag particles rom said alloy and then casting said alloy while preventing remixture of said alloy and slag.

4. The method of refining silicon steel which consists in subjecting said steel at a temperature above the melting point in contact with a slag to a periodically varying magnetic field applied from above said 'steel, thereby causing impurities in said steel to be incorporated into the slag and finally separating the metal and slag while maintaining said slag undisturbed.-

5. The method of refining ferrous metal CHARLES A. SOHARSCHU. 

